A major problem and expense during the refining of oil and other petroleum products is the continuous contamination of solid, porous catalysts by various porphyrins, metalloporphyrins, chlorins, and natural degradation products of these compounds, such as petroporphyrins, containing metals such as vanadium and nickel. Catalyst contamination is a major problem during refining and leads to loss of catalytic efficiency, which in turn demands the catalytic process be interrupted to either replace or clean the catalyst at a huge cost. The direct, material cost of replacing contaminated catalysts for the United States petroleum industry is estimated at more than $1 billion, annually.
Porphyrins, metalloporphyrins, chlorins, and the natural degradation products of these compounds, such as petroporphyrins, are referred to as simply porphyrins or metalloporphyrins from here forward. The term uncatalyzed is used to mean the state of liquid fuel before being subjected to cracking catalysis, a common step during the petroleum refining process here forward. Thus, uncatalyzed fuels mean uncracked fuels in the usual sense.
Contamination of petroleum catalysts occurs simultaneously via porphyrins and coke deposition on the catalyst surface. The coke contaminant is primarily carbon and may be removed from the catalyst by several simple means with regeneration of much lost catalytic activity. The porphyrins deposits, however, consists of several different metals on the catalytic surface including vanadium (V), nickel (Ni), titanium (Ti), iron (Fe), copper (Cu) or a combination thereof with the concentrations of V and Ni varying from a few to several hundred parts per million (ppm), depending on the type of crude oil supply. The functional lifetime of the catalyst is inversely proportional to the amount of contaminating metal deposited on that catalyst, so the gradual deposition of these metals on to the catalytic surface leads to eventual loss of catalytic power. Vanadium is usually present in a concentration greater than other metals with much more than half of all V being deposited on the catalyst arising from the porphyry complex. So removal of just the vanadium porphyrins from the crude oils would be commercially important.
Metal deposition is thought to proceed when contaminating metalloporphyrins bind near or at the catalytic site, becoming degraded after a short time, leaving the contaminating metal at the catalytic site which irreversibly deactivates the catalyst. It has been shown by observations using electronic spectroscopy that oxovanadium porphyrins bind to specific sites on two types of catalysts. Others have reported similar results of specific physical interactions between vanadium porphyrins and catalysts. The resulting metal complexes from petroleum contaminants with catalysts, primarily V and Ni, cannot be economically removed and eventually destroy the catalytic capability of the catalyst over time. In the end, the spent catalyst must be discarded and is currently deemed hazardous waste.
Reclamation of the spent catalyst, if performed at all, is both expensive and time consuming. Some microorganisms have been shown capable of removing some of the contaminating porphyrins and/or metals but these methods take several days to weeks to apply. These types of reclamations demand first rinsing the petroleum from the catalyst before application and then re-introduction of the petroleum via solvent exchange, taking time and labor. A variation of the method using the microorganism Aspergillus requires an expensive buffer salt for proper results. Chemical methods are also time consuming and take several steps, but only partly rejuvenate the catalytic function.